Operando Neutron Characterization of Metal Additive Manufacturing

Residual stress is ubiquitous in materials processing. Complex thermal conditions in metal additive manufacturing (AM) produce similarly complex distributions of residual stress, which can further interact with microstructure and phase transformations in unexpected ways. These interactions are challenging to observe during processing, and most studies rely on post-mortem analysis. In this work, a team at ORNL developed a wire-arc additive manufacturing (WAAM) system for operando neutron diffraction characterization at the VULCAN beamline in ORNL’s Spallation Neutron Source. The system including the WAAM manufacturing platform, the ability for active cooling in the substrate using compressed air, and complementary sensing with optical and infrared cameras. This presentation will describe how the system, dubbed OpeN-AM, was used to understand the interactions between process dynamics, phase transformations, and residual stress evolution in a martensitic low-temperature transformation (LTT) steel. Results from these experiments will be presented, as well as future directions for understanding and manipulating residual stress in AM.